functional bionic arm

this model is a bionic arm and hand with the following functions 

• 5 working fingers that all move independently from simply pulling a string 
• articulated elbow joint with string routes 
• fully modular desing for easy replacement and customization of the model
• fully printable version[not tested fully] 
• version with large parts substituted for wooden and pvc pipe components to lower cost

build process 

Me and my brother created this model for a school project on tinkercad we started with the fingers going through a couple of versions and adding a rubber band to pull the finger to strait and some 2.5mm thick cord to pull them in to grab stuff.

we used a small piece of 6mm plywood to create the palm for more easy customization as we could simply remove the 5 m4 bolts to remove the fingers and then modify the shape and finger placement to optimize the design this was the process that we went trough to create the hand design then we moved onto the arm.

this started by creating a wrist joint that would attach to the plywood palm via 2 m6 bolts and nuts it then slid into the forearm a simple pvc pipe with internal diameter of about 62mm to create the forearm the the elbow was modeled to be articulated and have 5 small pulley wheels to allow for the strings to be pulled from the top of the arm regardless of the elbow position we then attached another string to the pvc pipe to limit the movement of the elbow

we also added the fingertips from a rubber glove for extra grip

Assembly and printing

as you can see if you look at the print profiles there are many available options of what you can choose to print the options are listed below :

• to attach to 6mm plywood
  • single finger (Needs 1 m4x25mm bolt+nut and 1 rubberband and lenth of 2.5mm string)
  • all fingers[4 fingers+thumb] (Needs 5 m4x25mm bolt+nut and 5 rubberband and lenths of 2.5mm string)
• to attach to 62mm internal diameter pvc pipe
  • wrist part(needs 2 m6 by 30+mm+nuts lenth and hot glue+gun) 
  • elbow joint (needs 1 m4x70mm bolt and nut and some 2.5mm string)
• fully printable version (still needs all bolts, nuts, string and rubber bands) 

Finger assembly 

1. Remove all supports 
2. get the large rectangular base part and slide a joint inbetween the 2 triangles 
3. then insert a pin to connect them together 
4. reapeat with the other joint and the fingertip
5. push the string through the hole in the fingertip and tie off then slide it through the loop on the bottom of the base
6. connect a rubberband to the 2 loops on the top of the finger 

Hand assembly 

1. after creating a palm of any shape you desire or printing one slide the fingers into place 
2. if you are making a custom wood palm drill holes that line up with the hgoles on the finger base 
3. insert the 5 m4 bolts and add nuts
4. connect the wrist in the same way

Arm assembely 

1. insert the large circular end of the wrist into a lenth of pvc pipe (mine was 30cm long)
2. glue in place
3. thread string through
4. attach the elbow pieces to the other end of that pvc length and anoher lenth in the same way
5. place a long m4 bolt through the holes in the triangles and all the small pulley wheels 
6. thread the string through this assembly goiung through the pulley wheels
7. add a limiter string to the elbow joint and add a string to pull the elbow up going through a hol;e in the upper arm 
8. label the string ends so you know what connects to what

if anyone has any questions or feedback please comment